RF　 System for Bunch Rotation

C. Ohmori　（ KEK)

Bunch Rotation in Longitudinal Phase Space

Direction of Beam

Momentum

Injection to FFAG Large p/p

ApplyRF Voltage @ 5MHz

After several turns in FFAGSmall p/p

Saw Tooth RF is considered for smaller p/p

Low Frequency for Large Bucket vs. Difficulty to get High Voltage at Low Frequency

Saw-tooth

• PRISM-low energy muon (68 MeV/c) => 200 kV/m ＠ 5 MHz

• Scaling FFAG for Neutrino Factory – high energy muon (200 MeV/c)

• Bunch Merging Scenario for muon collider

PRISM• 200kV/m @ 5 MHz• MA cavity X Tube AMP:1 k X 60A/.33 m,

66kV/gap• Core impedance : about 160 /core X 6 cores• Tube AMP : OK, obtained >60 A as RF current

– Optimum design for only pulse operation (duty <0.1%)– Tubes is operated with Class B for 10 s, other;Class C.– 1 APS for 4 RF AMP.

• Tested with a test cavity and 43 kV/gap was obtained

• Saw-tooth RF is tested.

MA core for PRISM

1.7 m

PRISM Cavity Design

APS

AMP

Cavity

Beam Pipe

Side View

33cm

PRISM

But cost is expensive. cores >> AMP+PS

And, prefer more voltage for more muons.200kV/m => 300 kV/m

SolutionImprovement of Cavity (core) impedance

Other approach: ceramic cavity

Improvements of cavity impedance

• Hybrid cavity with ceramic cavity

• Improvements of cavity cores– X 2 by annealing

under magnetic field for thinner ribbon

– Small cores : OK

– Large core ?

uQf (é•ê´ëÃÉRÉAÇÃì¡ê´Åj

0

2

4

6

8

10

12

14

0 1 2 3 4 5 6

frequencyÅ@ÅiMHÇöÅj

uQf (GHz)

uQf(FT3L,13um)uQf(FT3L,18um)uQf(FT3M,18um)

How to improve • MA consists of Fe, Si, B, Cu and Nb.

• Amorphous ribbon (<20 m) is annealed and crystallized.

• Combination of magnetic field during annealing and thinner ribbon (13 m)

• The small crystal has an axis magnetized easily. By the special annealing, the axis is equal.

• But relation between core impedance and this effect is not clear.

• Small cores : proved by Hitachi Metal

• Large core : need big magnet and special oven. => Appling FY2007 JSPS money to produce these special core in KEK.

B-H curve of MA core produced by annealing with/without magnetic field.(by Hitachi Metal)

Ceramic Cavity • Proposed by J. Griffin.• Low frequency air core cavity with a ceramic capacitor to re

sonate.• Titanium Oxide capacitor was tested. 50kVDC (tested with

60kVDC). 1200pF. Electrodes are O.D. 121mmX I.D. 52mm, Thickness of ceramic is 14mm.

• Supported by JSPS money. Purpose : bunch rotation with low rep. rate.

• Small test cavity :30 cm X 30cm• 4 k, Q=700, fres=7 MHz• High power test is planned. • High rep. rate : Hybrid cavity system with MA cavity.

– Effective Q => below 100.